Grease composition

ABSTRACT

The grease composition including: a base oil having a kinematic viscosity of 5 to 30 mm 2 /s at 100° C., a thickener, a polymer having a weight average molecular weight of 1,000 to 500,000, and an aliphatic amide compound. The grease composition is used for sliding between a metal member and a resin member, and capable of reducing friction between them.

TECHNICAL FIELD

The present invention relates to a grease composition used between a metal member and a resin member.

RERATED ART

Grease compositions are mostly used for slide bearings and rolling bearings, or surfaces on which an oil film is hardly kept attached. The members constituting the surface is mainly made of a metal, but in recent years, a resin material is used in some cases for a part of the surface member for the purpose of saving weight. However, in addition to differences of friction and wear modes between a sliding between a metal member and a resin member and a sliding between metal members, the adsorption of a grease composition to the surface and appearance of additive reactions are different. For this reason, when a grease composition suitable for sliding between metal members is simply adopted to the surface between a metal member and a resin member, the expected performance may not be achieved.

There is a proposal of a grease composition used between a metal member and a resin member, which contains a base oil, a diurea compound as a thickener, and a chain hydrocarbon polymer having a weight average molecular weight of 20,000 to 30,000 (International Publication No. WO2016/104812).

However, in recent years, further reduction of friction is also required for the grease composition used at surfaces in order to enhance energy saving at surfaces such as bearings.

An object of the present invention is to provide a grease composition capable of reducing friction between a metal member and a resin member.

SUMMARY OF INVENTION

The present inventor conducted extensive studies to achieve the above object and consequently found that a base oil used with a thickener, an aliphatic amide compound, and a polymer can provide a grease composition suitable for sliding between a metal member and a resin member and capable of reducing friction.

The present invention has been accomplished based on such findings and includes the followings.

-   -   <1> A grease composition including: a base oil having a         kinematic viscosity of 5 to 30 mm²/s at 100° C., a thickener, a         polymer having a weight average molecular weight of 1,000 to         500,000, and an aliphatic amide compound, wherein the grease         composition is used for sliding between a metal member and a         resin member.     -   <2> The grease composition according to <1>, wherein the         aliphatic amide compound is a saturated aliphatic amide         compound.     -   <3> The grease composition according to <1> or <2>, wherein the         thickener is a urea-based thickener.     -   <4> The grease composition according to <3>, wherein the         urea-based thickener is a diurea compound represented by the         following formula (1):

R¹—NHCONH—R²—NHCONH—R³  (1)

wherein R¹ and R³ represent an aliphatic hydrocarbon group having 4 to 24 carbon atoms and optionally having a substituent, an alicyclic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, or an aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, and R² represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent.

-   -   <5> The grease composition according to any one of <1> to <4>,         wherein the base oil includes a poly-α-olefin.

The grease composition of the present invention provides a prominent effect of reducing friction in sliding between a metal member and a resin member.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail in line with preferable embodiments. In the present description, unless otherwise stated, the description “X to Y” means “X or more and Y or less.” In such a description, when a unit is provided only for a numerical value Y, the same unit should also be applied to a numerical value X.

The grease composition of the present invention includes a base oil, a thickener, a polymer having a weight average molecular weight of 1,000 to 500,000, and an aliphatic amide compound.

Base Oil

The base oil of the present invention can be a mineral oil or a synthetic oil. The kinematic viscosity at 100° C. of the base oil is 5 to 30 mm²/s, preferably 8 mm²/s or more, and more preferably 10 mm²/s or more, and preferably 27 mm²/s or less, and more preferably 25 mm²/s or less. In an embodiment, the kinematic viscosity at 100° C. is preferably 8 to 27 mm²/s, and more preferably 10 to 25 mm²/s. When a kinematic viscosity at 100° C. is the above lower limit value or more, the friction between a metal member and a resin member can be reduced, whereas when such a kinematic viscosity is the above upper limit value or less, the low temperature fluidity of the grease composition improves.

The kinematic viscosity at 40° C. of the base oil of the present invention is, for the same reason as the kinematic viscosity at 100° C., preferably 40 mm²/s or more, and more preferably 60 mm²/s or more, and preferably 300 mm²/s or less, and more preferably 230 mm²/s or less. In an embodiment, the kinematic viscosity at 40° C. is preferably 40 to 300 mm²/s, and more preferably 60 to 230 mm²/s.

In the present description, the kinematic viscosity at 100° C. or 40° C. respectively mean the kinematic viscosity at 100° C. or 40° C. measured according to JIS K2283:2000.

The viscosity index of the base oil of the present invention is preferably 90 or more, and more preferably 120 to 150. The pour point is preferably -10° C. or less, and more preferably -15° C. or less. The flash point is preferably 200° C. or more.

In the present description, the viscosity index means the numerical value obtained according to JIS K2283:2000, the pour point is according to JIS K2269:1987, and the flash point is according to JIS K2265-4:2007, respectively.

Examples of the mineral oil include base oil fractions obtained when a distillate obtained by distilling crude oil at atmospheric pressure, or further distilling such a distillate under reduced pressure, is refined by various refining processes. The refining process includes hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid treatment, clay treatment and the like, and a mineral oil can be obtained by combining these processes in a suitable order. Also useful is a mixture of more than one refined oil with different properties obtained by treating different crude oils or distillates by a combination and order of different processes. Any methods can be preferably used by adjustment so that properties of a base oil to be obtained satisfy the physical properties described above.

Base materials with excellent hydrolytic stability are preferably used as the synthetic oil. Examples include polyolefins such as poly-α-olefin, polybutene, and copolymers of two or more various olefins, ester-based synthetic oils such as diester and polyolester, ether-based synthetic oils such as alkyl diphenyl and polypropylene glycol, and polyalkylene glycol, alkyl benzene, alkyl naphthalene and the like. Of these, poly-α-olefin is preferable in the aspect of oxidative stability and low temperature fluidity.

For the base oil, the synthetic oils described as the examples can be used singly, or two or more can be used in mixture. Further, the synthetic oil can also be used by mixing with the mineral oil described above.

When a mixture of more than one base oil including a synthetic oil is used, the base oil mixture can be used as long as the above physical properties are satisfied even when respective base oils have such physical properties that are out of the ranges. Thus, respective synthetic base oils do not necessarily satisfy the above physical properties but preferably have the above physical properties within the ranges.

The content of the base oil is, on a total amount of the grease composition basis, preferably 50 mass % or more, and more preferably 60 mass % or more, and preferably 95 mass % or less, and more preferably 85 mass % or less. In an embodiment, the content of the base oil is preferably 50 to 95 mass %, and more preferably 60 to 85 mass %. When a content of the base oil is the above lower limit value or more, moderate lubricity can be assured, whereas such a content is the above upper limit value or less, the base oil is more likely to be retained in the grease composition.

Thickener

Both of a urea-based thickener and a metal soap-based thickener can be used as the thickener of the present invention.

<Urea-Based Thickener>

Usable urea-based thickener includes, for example, a diurea compound obtained by the reaction of diisocyanate and monoamine, a polyurea compound obtained by the reaction of diisocyanate, monoamine, and diamine and the like.

Diisocyanate is a compound in which two hydrogens in a hydrocarbon are substituted with isocyanate groups. The hydrocarbon may be acyclic hydrocarbon or cyclic hydrocarbon, and may be any of aromatic hydrocarbon, alicyclic hydrocarbon, and aliphatic hydrocarbon. The number of carbon atoms in the hydrocarbon is preferably 6 to 15, and more preferably 8 to 14. Preferable specific examples of diisocyanate include phenylene diisocyanate, tolylene diisocyanate, biphenyl diisocyanate (diphenyl diisocyanate), diphenylmethane diisocyanate, hexane diisocyanate, and decane diisocyanate. Diisocyanates may be used singly, or two or more may be used in combination.

Monoamines preferably used are aliphatic amines in which one hydrogen in an ammonia is substituted with an aliphatic hydrocarbon group having 4 to 24 carbon atoms, an alicyclic amine in which one hydrogen in an ammonia is substituted with an alicyclic hydrocarbon group having 6 to 15 carbon atoms, or an aromatic amine in which one hydrogen in an ammonia is substituted with an aromatic hydrocarbon group having 6 to 15 carbon atoms. The substituents of the aliphatic amines, alicyclic amines, and aromatic amines may further have substituents, respectively.

Preferable specific examples of monoamine include octylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, aniline, p-toluidine, and cyclohexylamine. Preferable specific examples of diamine include ethylene diamine, propane diamine, butane diamine, hexane diamine, octane diamine, phenylene diamine, tolylene diamine, xylene diamine, and diaminodiphenyl methane.

The urea-based thickener can be obtained by the reaction of the above diisocyanate and monoamine and is preferably a diurea compound represented by the following formula (1).

(Chemical formula 1)

R¹—NHCONH—R²—NHCONH—R³  (1)

wherein R¹ and R³ represent an aliphatic hydrocarbon group having 4 to 24 carbon atoms and optionally having a substituent, an alicyclic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, or an aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, and R² represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent.

When R¹ and R³ are aliphatic hydrocarbon groups, the number of carbon atoms thereof is preferably 8 to 18, when R¹ and R³ are alicyclic hydrocarbon groups, the number of carbon atoms thereof is preferably 6 to 12, and when R¹ and R³ are aromatic hydrocarbon groups, the number of carbon atoms thereof is preferably 7.

At least either one of R¹ and R³ is, same or different, preferably an alicyclic hydrocarbon group from a viewpoint of increasing a drop point of the grease composition.

<Metal Soap-Based Thickener>

A single soap and a complex soap are used as the metal soap-based thickener. The single soap is a metal soap obtained by saponifying a fatty acid or a fat/oil with an alkali metal hydroxide or an alkali earth metal hydroxide or the like. The complex soap is a complex obtained by further combining, in addition to the fatty acid used in the single soap, an organic acid having different molecular structure.

The fatty acid may be a fatty acid derivative having a hydroxy group and the like. The fatty acid is preferably a monovalent or divalent aliphatic carboxylic acid. The fatty acid is preferably aliphatic carboxylic acid having 6 to 20 carbon atoms, and more preferably monovalent aliphatic carboxylic acid having 12 to 20 carbon atoms or divalent aliphatic carboxylic acid having 6 to 14 carbon atoms. The fatty acid is preferably monovalent aliphatic carboxylic acid including one hydroxy group. The organic acid combined with the fatty acid in the complex soap is preferably acetic acid, diprotic acid such as azelaic acid or sebacic acid, or aromatic acid.

The metal of metal soap-based thickener usable includes alkali metals such as lithium and sodium, and alkali earth metals such as calcium, or amphoteric metals such as aluminum.

The thickener may be blended in the form of metal soap, but carboxylic acid and a metal source (metal salts, metal salt hydroxides and the like) may be separately blended and reacted when producing a grease to form a metal soap thickener.

Such carboxylic acid metal salts may be used singly, or more than one kind may be used in mixture. For example, a mixture of lithium 12-hydroxystearate and lithium azelate is preferable.

The thickener of the present invention may be used singly, or more than one kind may be used in mixture. The content of the thickener which may obtain desired penetration is, for example, on a total amount of the grease composition basis, preferably 2 to 30 mass %, and more preferably 5 to 20 mass %. The thickener preferably used is a urea-based thickener from a viewpoint of heat resistance at high temperatures and lubricity of the thickener itself.

Polymer

The polymer of the present invention has a weight average molecular weight of 1,000 to 500,000. The weight average molecular weight is preferably 2,000 or more, more preferably 5,000 or more, further preferably 100,000 or more, and preferably 450,000 or less, more preferably 400,000 or less, and further preferably 300,000 or less. In an embodiment, the weight average molecular weight is preferably 2,000 to 450,000, more preferably 5,000 to 400,000, and further preferably 100,000 to 300,000. When a weight average molecular weight is the above lower limit value or more, the lubricity of the grease composition improves, whereas a weight average molecular weight is the above upper limit value or less, low temperature fluidity improves.

In the present description, the weight average molecular weight of the polymer means the value determined by gel permeation chromatography (GPC) (molecular weight obtained by polystyrene conversion). The measurement conditions are as follows.

[GPC Measurement Conditions]

-   -   Device: ACQUITY ® APC UV RI system, manufactured by Waters         Corporation     -   Columns: in the order from the upstream side, two columns of         ACQUITY ® APC XT900A (gel particle size 2.5 μm, column size         (inner diameter x length) 4.6 mm×150 mm), manufactured by Waters         Corporation, and 1 column of ACQUITY ® APC XT200A (gel particle         size 2.5 μm, column size (inner diameter×length) 4.6 mm×150 mm),         manufactured by Waters Corporation, were serially connected     -   Column temperature: 40° C.     -   Sample solution: Sample concentration 1.0 mass % of         tetrahydrofuran solution     -   Flow rate: 0.8 mL/min     -   Detector: Differential refractive index detector     -   Reference substance: Standard polystyrene (Agilent EasiCal ®         PS-1, manufactured by Agilent Technologies) 8 samples (molecular         weights: 2698000, 660500, 325600, 128600, 69650, 30230, 9960,         2980)

The polymer of the present invention is not limited to the following examples but is, for example, an ethylene-α-olefin copolymer, poly(meth)acrylate, a styrene-diene copolymer, polybutene and the like.

<Ethylene-α-olefin Copolymer>

The ethylene-α-olefin copolymer includes, as monomer units, ethylene and an a-olefin having 3 or more carbon atoms. Examples of the a-olefin having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, and 1-decene, with propylene being preferable.

The content of the ethylene unit in an ethylene-α-olefin copolymer is, on a total amount of the monomer unit basis, may be, for example, 30 to 80 mol %, 35 to 75 mol %, or 40 to 70 mol %. The content of the a-olefin unit in an ethylene-α-olefin copolymer is, on a total amount of the monomer unit basis, may be, for example, 20 to 70 mol %, 25 to 65 mol %, or 30 to 60 mol %.

<Poly(meth)acrylate>

The poly(meth)acrylate preferably contains a structural unit represented by the following formula (2). In the present description, “(meth)acrylate” means “acrylate and/or methacrylate.”

wherein R⁴ represents hydrogen or a methyl group, R⁵ represents a linear or branched hydrocarbon group having 1 to 18 carbon atoms.

In an embodiment, R⁵ is a hydrocarbon group having 1 to 5 carbon atoms or a hydrocarbon group having 6 to 18 carbon atoms, or a combination thereof.

<Styrene-diene Copolymer>

The styrene-diene copolymer includes, as monomer units, one or more styrene-based monomers selected from styrenes and hydrides thereof, and one or more diene-based monomers selected from dienes and hydrides thereof. The dienes usable are, for example, butadiene and isoprene.

The content of the styrene-based monomer unit in the styrene-diene copolymer may be, on a total amount of the monomer unit basis, for example, 1 to 30 mol %, or 5 to 20 mol %. The content of the diene monomer unit in the styrene-diene copolymer may be, on a total amount of the monomer unit basis, for example, 70 to 99 mol %, or 80 to 95 mol %.

<Polybutene>

Polybutene is a polymer obtained by polymerizing butenes having a double bond. The polybutene may be a polymer represented by, for example, the following formula (3).

wherein n represents an integer of 5 to 90.

The polybutene usable may be a commercial product as it is, or polybutene produced by a known method. The method for producing the polybutene is, for example, a method of removing butadiene from C4 fraction generated by naphtha cracking and polymerizing the butadiene using an acid catalyst.

The polymer of the present invention may be used singly, or two or more polymers may be used in combination. The polymer is preferably an ethylene-α-olefin polymer from a viewpoint of reducing friction of the grease composition.

The polymer of the present invention usable may be a pure product, or a diluted product in a state diluted to a light oil such as kerosene and diesel oil.

The content (not including a diluting oil) of the polymer is, on a total amount of the grease composition basis, preferably 0.1 mass % or more, more preferably 0.2 mass % or more, and further preferably 0.4 mass % or more, and preferably 10 mass % or less, more preferably 8 mass % or less, and further preferably 6 mass % or less. In an embodiment, the content of the polymer is preferably 0.1 to 10 mass %, more preferably 0.2 to 8 mass %, and further preferably 0.4 to 6 mass %. When a content range of the polymer is the above lower limit value or more, friction between a metal member and a resin member further reduces, whereas when such a content is the above upper limit value or less, low temperature fluidity of the grease composition improves.

Aliphatic amide compound

The aliphatic amide compound used in the present invention is aliphatic monoamide having one amide group (—NH—CO—), aliphatic bisamide having two amide groups, aliphatic triamide having three amide groups and the like.

The monoamide may be either acid amide of monoamine or acid amide of mono acid. The bisamide may also be either acid amide of diamine or acid amide of diacid.

Aliphatic amide compounds preferably used are those having a melting point of 40 to 180° C., more preferably 80 to 180° C., and further preferably 100 to 170° C., and a molecular weight of 242 to 932, and more preferably 298 to 876.

The aliphatic monoamide, aliphatic bisamide, and aliphatic triamide are represented respectively by the following formulae (4), (5) or (6), and (7).

R⁶—CO—NH—R⁷  (4)

R⁶—CO—NH—A¹—NH—CO—R⁷  (5)

R⁶—NH—CO—A¹—CO—NH—R⁷  (6)

R⁶—M—A¹—CH(A²—M—R⁷)—A³—M—R⁷  (7)

In each of the above formulae, R⁶ and R⁷ are each independently an aliphatic hydrocarbon group having 5 to 25 carbon atoms. In formula (4), a case where R⁷ is hydrogen is included. The number of carbon atoms of R⁶ and R⁷ is preferably 10 or more, and more preferably 15 or more, and preferably 20 or less, and more preferably 17 or less. In an embodiment, the number of carbon atoms of R⁶ and R⁷ is preferably 10 to 20, and more preferably 15 to 17. When a number of carbon atoms of R⁶ and R⁷ is the above lower limit value or more, friction between a metal member and a resin member even more reduces, whereas such a number of carbon atoms is the above upper limit value or less, low temperature fluidity of the grease composition improves.

A¹, A², and A³ are each independently an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or an aromatic hydrocarbon group having 1 to 10 carbon atoms, or a divalent hydrocarbon group in the form of combination of these groups and having 1 to 10 carbon atoms, and M is an amide group (—NH—CO—, or —CO—NH—).

When the aliphatic amide compound is monoamide, R⁷ is preferably hydrogen or an aliphatic hydrocarbon group having 10 to 20 carbon atoms.

When the aliphatic amide compound is acid amide of diamine, A¹ is preferably a divalent saturated chain hydrocarbon group having 1 to 4 carbon atoms.

In the hydrocarbon group represented by R⁶, R⁷, or A¹ in formulae (5) and (6), a part of the hydrogens may be substituted with a hydroxyl group (—OH).

The aliphatic monoamide is specifically substituted amides with saturated or unsaturated long chain fatty acid and long chain amine such as saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide, unsaturated fatty acid amides such as oleamide and erucic acid amide, and stearyl stearic acid amide, oleyl oleamide, oleyl stearic acid amide, and stearyl oleamide.

The acid amide of diamine represented by formula (5) specifically includes ethylene bis stearic acid amide, ethylene bis isostearic acid amide, ethylene bis oleamide, methylene bis lauric acid amide, hexamethylene bis oleamide, hexamethylene bis hydroxystearic acid amide and the like. The bisamide of diacid represented by formula (6) specifically includes N,N′-bis stearyl sebacic acid amide and the like.

The aliphatic amide compound of the present invention is preferably saturated aliphatic amide in which at least one of R⁶ and R⁷ is a saturated aliphatic hydrocarbon group from a viewpoint of reducing friction.

The aliphatic amide compound is preferably aliphatic bisamide or aliphatic triamide from a viewpoint of reducing friction, with aliphatic bisamide being more preferable.

The aliphatic amide compound of the present invention may be used singly, or two or more may be used in combination. The content of the aliphatic amide compound is, on a total amount of the grease composition basis, preferably 1 mass % or more, more preferably 2 mass % or more, and further preferably 4 mass % or more, and preferably 30 mass % or less, and more preferably 20 mass % or less, and further preferably 15 mass % or less. In an embodiment, the content of the aliphatic amide compound is preferably 1 to 30 mass %, more preferably 2 to 20 mass %, and further preferably 4 to 15 mass %. When the content of the aliphatic amide compound is the above lower limit value or more, friction between a metal member and a resin member even more reduces, whereas when such a content is the above upper limit value or less, low temperature fluidity of the grease composition improves.

When the aliphatic amide compound is heated and dissolved in the presence of the base oil, the base oil is retained in the amide compound forming a three-dimensional network structure and friction between a metal member and a resin member reduces as compared with the case where the amide compound is simply dispersed and mixed in a grease.

Other Additives

In the grease composition of the present invention, a solid lubricant, an anti-wear agent or an extreme pressure agent, an antioxidant, a friction modifier, an anti-rust agent, a corrosion inhibitor and the like that are generally used for lubricants and greases can be suitably added as needed in addition to the above components.

The solid lubricant is, for example, graphite, graphite fluoride, melamine cyanurate, polytetrafluoroethylene, molybdenum disulfide, antimony sulfide, boron nitride, alkaline (earth) metal borate and the like. When the grease composition contains a solid lubricant, the content thereof is, on a total amount of the grease composition, typically 0.1 to 20 mass %.

The anti-wear agent or an extreme pressure agent is, for example, organozinc compounds such as zinc dialkyldithiophosphate, and zinc dialkyldithiocarbamate, sulfur-containing compounds such as molybdenum dialkyldithiocarbamate, dihydrocarbyl polysulfide, sulfurized ester, thiazole compounds, and thiadiazole compounds; phosphorus-based extreme pressure agents such as phosphoric acid ester, acidic phosphoric acid ester, amine salts of acidic phosphoric acid ester, and phosphorous acid ester. When the grease composition contains an anti-wear agent or an extreme pressure agent, the content thereof is, on a total amount of the grease composition basis, typically 0.1 to 10 mass %.

The antioxidant is, for example, phenol-based compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol, amine-based compounds such as diphenylamine, dialkyl diphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the grease composition contains an antioxidant, the content thereof is, on a total amount of the grease composition basis, typically 0.5 to 10 mass %, and preferably 1 to 5 mass %. The antioxidant may include both of a phenol-based compound and an amine-based compound.

The friction modifier is, for example, amines such as lauramine, myristamine, palmitamine, stearamine, oleamine and the like; higher alcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and oleyl alcohol; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; fatty acid esters such as lauric acid methyl ester, myristic acid methyl ester, palmitic acid methyl ester, stearic acid methyl ester, and oleic acid methyl ester; fats/oils such as glyceryl oleate and glyceryl stearate. When the grease composition contains a friction modifier, the content thereof is, on a total amount of the grease composition, typically 0.01 to 5 mass %.

The anti-rust agent is, for example, amines, neutral or ultrabasic petroleum or synthetic oil-based metal sulfonate, metal carboxylates, esters, phosphoric acid, and phosphate. When the grease composition contains an anti-rust agent, the content thereof is, on a total amount of the grease composition basis, typically 0.005 to 5 mass %.

The corrosion inhibitor usable is, for example, known corrosion inhibitors such as benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, and imidazole-based compounds. When the grease composition contains a corrosion inhibitor, the content thereof is, on a total amount of the grease composition basis, typically 0.01 to 10 mass %.

Grease Composition

The penetration of the grease composition of the present invention is, from a viewpoint of fluidity and easiness in staying of a grease at a surface, 175 to 385, and more preferably 220 to 340. Penetration indicates physical hardness of a grease.

The penetration in the present description means the worked penetration measured according to JIS K2220:2013.

The drop point of the grease composition of the present invention is, from a viewpoint of maintaining durability of parts at high temperatures, preferably 180° C. or more, and more preferably 200° C. or more. Drop point refers to the temperature at which grease loses the thickener structure as raising temperature.

The drop point herein can be measured according to JIS K2220:2013.

Preparation Method

The grease composition of the present invention can be made by a general grease production method, but it is preferable that the aliphatic amide compound be heated once to a melting point or higher after mixed.

In other words, a method of heating an aliphatic amide compound and a base oil to the melting point of the aliphatic amide compound or higher, cooling and physically mixing with a grease composed of a thickener and the base oil may be employed, or a method of mixing all components including a thickener, then heating to the melting point of the aliphatic amide compound or higher, and cooling may also be employed.

Thus, when the aliphatic amide compound is heated once to the melting point of the aliphatic amide compound or higher in the presence of at least a base oil, the base oil is retained in the aliphatic amide compound forming a three-dimensional network structure thereby to be a semi-solid gel. Microscopically, the base oil is freely moving in the network structure. This indicates that, for example, when a gel composition having lubricity contacts porous narrow gaps, the capillary action enables the base oil in the gel to move from the gel to narrow gaps. Reversely, this indicates that when extra base oil is present in the system, the three-dimensional network structure of the gel induces the capillary action thereby to take in the extra base oil to the gel. The thickener imparts penetration due to such a condition thereby reducing friction at a surface.

<Materials to be Lubricated>

The grease composition of the present invention is preferably used for lubricating various resin surface members and metal surface members. Examples of the resin include polyamide resins, polycarbonate, polyamideimide resins, polyacetal resins, polybutylene terephthalate resins, and polyether ether ketone resins. The grease composition is particularly preferable for members in which polyamide resins are used. The metal surface members include bearing steel, carbon steel, stainless steel (SUS) and the like.

<Application of Grease Composition>

The grease composition of the present invention can be used for sliding between a metal member and a resin member such as generally used machines, bearings, gears, and ball screws, and can demonstrate excellent performance even under harsh environment. The grease composition can be used in automobile for lubricating the power train such as water pump, cooling fan motor, starter, alternator and various actuator parts near engine, propeller shaft, constant-velocity joint (CVJ), wheel bearing and clutch, and various parts such as electric power steering (EPS), electric power window, braking system, ball joint, door hinge, steering wheel, and brake expander. Further, the grease composition can also be used for various shafts and fitting parts that may involve reciprocating sliding movement such as construction machinery including excavator, bulldozer, and crane truck, steel industry, paper manufacturing industry, forestry machinery, agricultural machinery, chemical plant, power facility, and railway car. For other usages, the grease composition can also be used for threaded joint for seamless pipe, and bearing for outboard motor.

EXAMPLES

Hereinafter, the present invention will be described using examples as an embodiment of the present invention, but is not limited to the following embodiment.

A base oil, a thickener and each additive were blended in the blending ratios shown in Table 1 for each of Examples 1 to 11 and each of Comparative Examples 1 to 4 to prepare test grease compositions. Unless otherwise stated, the “mass %” in the table shows each blended amount on a total amount of the grease composition basis.

(1) Base Oil

Base oils 1 and 2 were mixed so that kinematic viscosities at 100° C. were values described in Table 1.

-   -   Base oil 1: poly-α-olefin (100° C. kinematic viscosity: 8.0         mm²/s, viscosity index: 136, pour point: <−45° C., flash point:         265° C.)     -   Base oil 2: poly-α-olefin (100° C. kinematic viscosity: 40.0         mm²/s, viscosity index: 149, pour point: <−30° C., flash point:         280° C.)

(2) Thickener

The thickener was diurea synthesized from monoamine and diphenylmethane diisocyanate (MDI). The monoamine was used by mixing cyclohexylamine (CHA) and/or octadecylamine (ODA) in the molar ratios shown in Table 1.

(3) Polymers

-   -   Polymer A: ethylene-propylene copolymer (weight average         molecular weight: 200,000, polymer concentration in diluting         oil: 10%)     -   Polymer B: ethylene-propylene copolymer (weight average         molecular weight: 300,000, polymer concentration in diluting         oil: 10%)     -   Polymer C: ethylene propylene copolymer (weight average         molecular weight: 60,000, no diluting oil)     -   Polymer D: styrene-diene copolymer (weight average molecular         weight: 440,000, polymer concentration in diluting oil: 10%)     -   Polymer E: polymethacrylate (weight average molecular weight:         400,000, polymer concentration in diluting oil: 20%)     -   Polymer F: polybutene (weight average molecular weight: 2,000,         no diluting oil)

(4) Aliphatic Amide Compound

-   -   Aliphatic amide: ethylene bis stearic acid amide

(5) Other Additives

-   -   Antioxidant: diphenylamine

Preparation Method

The amine and isocyanate to be raw materials of the thickener were reacted in the base oil so that the blending ratios were as shown in Table 1, followed by raising temperature and cooling thereby to obtain reactant 1. Further, the aliphatic amide compound was added to the same type of base oil taken in a different container from the previously described base oil, heated to 150° C. (the melting point of the aliphatic amide compound or higher), stirred in a magnetic stirrer and then cooled to room temperature thereby to obtain semi-solid reactant 2.

The reactant 1 and reactant 2 were mixed so that the blending ratios of the aliphatic amide compound were as shown in Table 1, and further the remaining additive was added in the blending ratios shown in Table 1. The mixture was kneaded using a three-roll mill thereby to obtain the test grease compositions shown in Table 1.

The obtained test grease compositions were evaluated as follows. The evaluation results are shown in Table 1.

Evaluation Method

<Friction Coefficient>

An evaluation test was performed using a ball-on-disk reciprocating tribometer. The ball (steel surface member) used was a SUJ-2 ball having a diameter of ¼ inches, and the disk (resin surface member) used was a 66 nylon plate (TPS ® N66 (NC) manufactured by Toray Plastics Precision Co., Ltd.).

The grease was applied to the disk to measure friction coefficient when sliding at room temperature (25° C.) under conditions of test force: 2000 gf, sliding speed: 10 mm/s, and amplitude: 20 mm.

Evaluation result

Comparative Example 1 which does not contain the polymer and the aliphatic amide compound showed high friction coefficient when sliding between a metal member and a resin member. Comparative Example 2 which contained only the polymer and Comparative Example 3 which contained only the aliphatic amide compound showed slightly more reduced friction than Comparative Example 1, which was however not sufficient.

To the contrary, it was revealed that the grease compositions of the present invention containing the polymer and the aliphatic amide compound showed sufficient reduction in friction when sliding between a metal member and a resin member (Examples 1 to 11). Comparative Example 4, in which the base oil has a kinematic viscosity at 100° C. of more than 30 mm²/s, had insufficient reduction in friction.

TABLE 1 Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 8 Base oil Kinetic 23.0 23.0 23.0 23.0 23.0 23.0 23.0 23.0 viscosity at 100° C. (mm²/s) Blending Balance Balance Balance Balance Balance Balance Balance Balance amount (mass %) Thickener CHA 25 25 25 25 25 25 25 100 (mol %) ODA 75 75 75 75 75 75 75 — (mol %) blended 11 9 11 9 11 9 9 9 amount (mass %) Polymer Polymer A 5 5 — — — — — 5 (mass %) Polymer B — — 5 — — — — — (mass %) Polymer C — — — 5 — — — — (mass %) Polymer D — — — — 5 — — — (mass %) Polymer E — — — — — 5 — — (mass %) Polymer F — — — — — — 5 — (mass %) Aliphatic amide 5 10 5 10 5 5 5 10 compound (mass %) Antioxidant (mass %) 2 2 2 2 2 2 2 2 Penetration — — — 315 — — — 332 Friction 0.026 0.030 0.025 0.026 0.029 0.030 0.031 0.024 coefficient Compar- Compar- Compar- Compar- ative ative ative ative Example Example Example Example Example Example Example 9 10 11 1 2 3 4 Base oil Kinetic 10.0 8.0 23.0 23.0 23.0 23.0 40.0 viscosity at 100° C. (mm²/s) Blending Balance Balance Balance Balance Balance Balance Balance amount (mass %) Thickener CHA 50 25 — 25 25 25 25 (mol %) ODA 50 75 100 75 75 75 75 (mol %) blended 12 11 — 13 13 12 11 amount (mass %) Polymer Polymer A 5 5 5 — 5 — 5 (mass %) Polymer B — — — — — — — (mass %) Polymer C — — — — — — — (mass %) Polymer D — — — — — — — (mass %) Polymer E — — — — — — — (mass %) Polymer F — — — — — — — (mass %) Aliphatic amide 5 5 5 — — 5 5 compound (mass %) Antioxidant (mass %) 2 2 2 2 2 2 2 Penetration — — — 294 310 — — Friction 0.039 0.030 0.028 0.054 0.046 0.050 0.053 coefficient

Industrial Applicability

The grease composition of the present invention has excellent low friction so that it is applicable for lubricating various joints, gears, bearings and the like having a surface between a metal member and a resin member. 

1. A grease composition comprising: a base oil having a kinematic viscosity of 5 to 30 mm²/s at 100° C., a thickener, a polymer having a weight average molecular weight of 1,000 to 500,000, and an aliphatic amide compound, wherein the grease composition is used for sliding between a metal member and a resin member.
 2. The grease composition according to claim 1, wherein the aliphatic amide compound is a saturated aliphatic amide compound.
 3. The grease composition according to claim 1, wherein the thickener is a urea-based thickener.
 4. The grease composition according to claim 3, wherein the urea-based thickener is a diurea compound represented by the following formula (1): R¹—NHCONH—R²—NHCONH—R³  (1) wherein R¹ and R³ represent an aliphatic hydrocarbon group having 4 to 24 carbon atoms and optionally having a substituent, an alicyclic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, or an aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, and R² represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent.
 5. The grease composition according to claim 1, wherein the base oil comprises a poly-α-olefin.
 6. The grease composition according to claim 2, wherein the thickener is a urea-based thickener.
 7. The grease composition according to claim 6, wherein the urea-based thickener is a diurea compound represented by the following formula (1): R¹—NHCONH—R²—NHCONH—R³  (1) wherein R¹ and R³ represent an aliphatic hydrocarbon group having 4 to 24 carbon atoms and optionally having a substituent, an alicyclic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, or an aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent, and R² represents a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms and optionally having a substituent.
 8. The grease composition according to claim 2, wherein the base oil comprises a poly-α-olefin.
 9. The grease composition according to claim 3, wherein the base oil comprises a poly-α-olefin.
 10. The grease composition according to claim 4, wherein the base oil comprises a poly-α-olefin.
 11. The grease composition according to claim 6, wherein the base oil comprises a poly-α-olefin.
 12. The grease composition according to claim 7, wherein the base oil comprises a poly-α-olefin. 